1. Field of the Invention
The present invention generally relates to semiconductor integrated circuits, and particularly relates to a semiconductor integrated circuit having pads thereof arranged in line.
2. Description of the Related Art
LSIs (larges-scale semiconductor integrated circuits) are provided with pads for the purpose of inputting/outputting signals from/to the exterior. As a single LSI chip is required to have an increased number of functions, the number of pads also increases due to an increase in the number of signal inputs/outputs. As the chip size decreases in response to improved circuit density, the size and pitch of pads need to be decreased in accordance with the reduction of chip size.
In particular, a numerous number of signal inputs/outputs are provided in a driver IC or the like that drives a liquid crystal display panel, resulting in a large number of pads being arranged at short intervals on a single LSI chip. These pads are generally arranged in line (such as to form a straight line).
FIG. 1 is an illustrative drawing showing a pad arrangement on an LSI such as a driver IC for driving a liquid crystal display panel.
On an LSI chip 10 shown in FIG. 1, a plurality of pads 11 are arranged in line so as to form two rows. FIG. 2 is an illustrative drawing showing an example of the size and layout of the pads 11.
As shown in FIG. 2, the pads 11 have a rectangular shape measuring 70 micrometers by 35 micrometers, and are arranged at 15-micrometer intervals. The pitch is 50 micrometers when it is defined as a distance between the centers of adjacent pads.
LSIs manufactured in factory undergo tests for checking operations prior to shipment. In such tests, probe needles are brought into contact with more than one pad to detect input/output signals corresponding to required test signals. Based on the output signals, a check is made as to whether the operations of LSIs are proper.
A probe needle has a diameter of approximately 15 micrometers, and positioning typically involves an error in the range of at least 5 micrometers. When a probe needle comes in contact with a pad, secure contact is necessary. Otherwise, improper contact will results in a failure of the test. Because of this, as shown in FIG. 2, the pad size of about 35 micrometers and the pad pitch of about 50 micrometers are close to the limits that ensure secure contact and avoid wrong contact with an adjacent pad. Probe needles may be made thinner so as to be usable for narrower pitch. This is not desirable, however, because of problems associated with the durability of needles.
Accordingly, there is a need for a semiconductor integrated circuit which has pads arranged at intervals narrower than necessary for proper measurement by a probe needle, but is provided with a mechanism that allows a probe needle to make secure contact with a pad.